Modified amine hardener systems

ABSTRACT

A resinous hardener system comprising the reaction product of diamino diphenylsulfone compounds and diglycidyl ethers of polyhydric phenols. The hardener system can be incorporated into a variety of epoxy resins for use as improved prepreg or laminating resins, as resin molded castings, and the like.

This application is a continuation-in-part of application Ser. No.194,094, filed Oct. 6, 1980, now abandoned.

Adducts from amines and mono- and diepoxides have long been used inindustry as curing agents for epoxy resins. The advantages of theformation of such adducts include lower volatility, lower irritationpotential, reduced tendency to blush and exude, and the like. Suchadducts are discussed in Lee and Neville, Handbook of Epoxy Resins,McGraw Hill (1967).

Such systems have frequently been used within the aerospace industry. Aprimary area of use has been in epoxy resins which are utilized topre-impregnate various fibers for eventual use as honeycomb skins. Thesevarious laminates are utilized in aerospace construction. The currently,most widely used epoxy system for prepregging and laminating is basedupon tetraglycidylated methylene dianiline and a diaminodiphenylsulfonehardener. While these systems have shown to advantage, they also haveexhibited a number of meaningful disadvantages. These disadvantages stemprimarily from the hardener's incompatibility with the resin and thedifficulty of dissolving it in the epoxy resin. Among the specificprocessing disadvantages are included:

1. the need for high temperatures in order to get the hardener intosolution without the need for extraneous solvents;

2. the undesirable advancement of the hardener with the epoxy, usuallyrequiring that other resins be added to increase the drape and tackwhich, in turn, usually lowers the melt viscosity;

3. the need for heat to remove any solvents which may be used, therebyresulting in some advancement; and

4. the difficulty of achieving and controlling the desired flow causingvariations of the prepreg within the same batch.

Although the resulting systems are operable and can be successfullylaminated, they too exhibit a number of disadvantages including:

1. They have a high modulus and are brittle.

2. They are moisture sensitive to some extent.

3. Reproducibility in the production of low--or no--bleed systems isdifficult to achieve.

4. It is difficult to prepare honeycomb core composites with thesesystems due to their poor flow characteristics which allow for bleedingof the resin into the core thereby causing void spaces in the skins.

It is the primary object of this invention to provide a modifiedhardener system for epoxy resins.

It is a further object to provide such a hardener system which improvesupon the performance of diamino diphenylsulfone hardeners.

It is another object to utilize such hardener systems with a widevariety of epoxy resins to provide prepreg or laminating resins ofimproved performance characteristics.

Various other objects and advantages of this invention will becomeapparent from the following descriptive material and illustrativeexamples.

It has now been surprisingly discovered that by reacting the diaminodiphenylsulfone with a diglycidyl ether of a polyhydric phenol theprocessing characteristics of the hardener system and the performancecharacteristics of the epoxy resin cured therewith are dramaticallyenhanced without adversely effecting, in a substantial way, the otherdesired properties. The latter characteristics are particularly evidentwhen the modified hardener is utilized in conjunction withtetraglycidylated methylene dianiline. Improved compatibility with theresin and increased melt viscosity resulting in a controllable flow arenoted. The resulting systems can be laminated or used in skins onhoneycombs and exhibit improved impact resistance, toughness, strengthand water resistance.

More specifically, the improved processing parameters include:

1. Increased compatibility of the hardener with the epoxy resin. Thehardener solubilizes at lower temperatures, reducing the chance of anundesired advancement. The chance of incomplete dissolution or mixing issimilarly reduced.

2. The melt viscosity of the system may be controlled by the molecularweight of the hardener. This eliminates the necessity fordifficult-to-control advancement steps in the preparation of the resinsystem.

3. The use of resin additives will still function in obtaining gooddrape and tack.

4. The advancement of the resin on the prepreg is easier to control dueto the reduced need for advancement.

5. The modified hardener allows reproducible production of no--orlow--bleed prepregs for use with or without honeycomb.

In addition, the resins cured with the instant hardener systems exhibitthe following improved properties:

1. Such systems are readily laminated.

2. They are tougher and have higher impact strength than theconventionally hardened systems.

3. They exhibit added mechanical strength.

4. They xhibit an increased humidity resistance.

5. They have a higher melt flow viscosity.

6. The instant systems are also vastly superior to rubber-modifiedsystems.

As a result of these delineated characteristics, the modified hardenersystem lends itself for use in primary composite structures, an area ofapplication in which the existing systems have not been able to performeffectively. The modified hardener system is also available for use witha broad range of difunctional and multifunctional epoxy resins for usein a wide area of applications such as coatings, molded castings,adhesives and filament wound structures.

The modified hardener system is prepared by adducting the epoxy resinwith the diamino diphenylsulfone compound. The applicable diaminodiphenylsulfones correspond to the formula ##STR1## wherein R₁, R₂, R₃and R₄ are independently hydrogen, straight and branched chain alkyl of1 to 12 carbon atoms, preferably 1 to 4 carbon atoms, or halogen.Commercially available sulfones include the 2,4'-, 3,3'- and4,4'-diamino diphenylsulfones. Although diamino diphenysulfones arepreferred for purposes of this invention, other aromatic polyamines oraralkyl polyamines can be utilized for the preparation of the instantadducts.

The applicable epoxy resins are diglycidyl ethers of polyhydric phenols.Among such materials are diglycidyl ethers of bisphenols correspondingto the formula ##STR2## wherein m is 0-50 and X is --CH₂ --, ##STR3##These represent, respectively, bisphenols F, A and S. Other applicableethers include the diglycidyl ethers of resorcinol, catechol,hydroquinone, and the like. The various ethers may be substituted on therespective phenyl rings by such non-reactive substituents as alkyl,halogen, and the like.

The general procedure for preparing the modified hardener involvesforming a solution of the diglycidyl ether in an appropriate solvent,admixing the sulfone, and heating the resulting mixture at a temperatureof about 130°-180° C. until completion of the reaction. Completion willgenerally take 2-6 hours and may be monitored by analytical procedures,completeness being indicated by the disappearance of the epoxy function.Solvent removal is generally effected by evaporation during furtherprocessing. Applicable solvents include ketones, aromatic hydrocarbonssuch as toluene, and the like. In some instances, the solvent may beomitted depending on the nature of the component blend.

It may be desirable to prepare the resin in-situ by co-reacting thediglycidyl ether with additional polyhydric phenol. In this instance,small amounts of an appropriate catalyst such as alkali metalhydroxides, tertiary amines, quaternary amines, and the like may beutilized.

Concentrations of the sulfone are selected so as to achieve a modifiedhardener system having from about 2.5 to 100 equivalents ofaminohydrogen per equivalent of epoxy. These values are selected intoorder to avoid gelling at levels lower than those specified and reducedphysical properties at levels higher than those specified.

As previously noted, the modified hardener systems can be processed witha wide variety of epoxy resins. Included among such resins are epoxideresins based on polyhydric phenols such as those based on bisphenol A,F, and S, epoxidation products of cresol novolacs, and epoxidationproducts of phenol novolacs; hydantoin epoxide resins; polyglycidylesters; glycidylated aromatic amines; glycidylated aminophenols; andcertain cycloaliphatic epoxy resins. Tetraglycidylated methylenedianiline is preferred for purposes of the instant invention. Inaddition, in adhesive, coating and filament winding applications, resinbased on the diglycidyl ether of bisphenol A is widely used. Themodified hardener is utilized in stoichiometric amounts ±50% relative tothe epoxy resin, with 85% of stoichiometry being preferred.

Techniques for preparing prepregs are well known to those skilled in theart. In terms of honeycomb skins, graphite, glass, Kevlar reinforcedskins as well as others, can be readily prepared from the instantsystems. Correspondingly, techniques for preparing laminates are wellknown. Such laminates may be prepared by compression or autoclavemolding and may comprise a broad range of thicknesses.

Apart from the above areas of utility, the adducts of this invention areuseful as curing agents for a wide variety of epoxy resins in variousheat cured applications. When combined with di- and polyepoxides, atgenerally stoichiometric amounts, and cured at elevated temperatures, anetwork of high crosslink density occurs. Accordingly, the expression"cure" as used herein, denotes the conversion of the above adducts andepoxide material into insoluble and infusible crosslinked products, withsimultaneous shaping to give shaped articles such as castings, pressingsor laminates, or to give two-dimensional structures such as coatings,enamels or adhesive bonds. The modified hardener system is particularlyadvantageous for the formation of coatings because of the improvedcompatibility with resins and the improved toughness of the resultingcured coatings.

The adducts prepared according to the invention and admixed with otherpolyepoxide compounds can furthermore be mixed, at any stage beforecure, with usual modifiers such as extenders, fillers and reinforcingagents, pigments, dyestuffs, organic solvents, plasticizers, tackifiers,rubbers, accelerators, diluents, and the like. As extenders, reinforcingagents, fillers and pigments which can be employed in the curablemixtures according to the invention there may be mentioned, for example:coal tar, bitumen, glass fibers, boron fibers, carbon fibers, cellulose,polyethylene powder, polypropylene powder, mica, asbestos, quartzpowder, gypsum, antimony trioxide, bentones, silica aerogel ("Aerosil"),lithopone, barite, titanium dioxide, carbon black, graphite, iron oxide,or metal powders such as aluminum powder or iron powder. It is alsopossible to add other usual additives, for example, flameproofingagents, agents for conferring thixotropy, flow control agents such assilicones, cellulose acetate butyrate, polyvinyl butyral, waxes,stearates and the like (which are in part also used as mold releaseagents) to the curable mixtures.

It is also possible in adhesive formulations, for example, to addrubbers such as carbonyl-terminated acrylonitrile-butadiene rubber,modifying resins such as triglycidyl p-aminophenol, accelerators such asboron trifluoride monoethylamine complexes or imidazole complexes, andother additional hardeners such as dicyandiamide.

The curable mixtures can be manufactured in the usual manner with theaid of known mixing equipment (stirrers, kneaders, rollers and thelike).

The following examples will further illustrate the embodiments of theinstant invention. In these examples, all parts given are by weightunless otherwise noted.

EXAMPLE I

The following example illustrates the preparation of typical modifiedhardeners of the instant invention.

    ______________________________________                                                   Hardener #1 Hardener #2                                                       Parts       Parts                                                  ______________________________________                                        Diglycidyl ether of                                                           bisphenol A.sup.1                                                                          100.0   0.530 epoxy                                                                             100.0 0.530 epoxy                              Bisphenol A  29.0    0.254 OH  29.0  0.254 OH                                 50% NaOH     0.008             0.008                                          After complete       0.276 epoxy     0.276 epoxy                              reaction                                                                      Methyl Ethyl ketone                                                                        86.0              86.0                                           Diamino diphenyl-                                                                          160.0   2.581 NH  129.0 2.081 NH                                 sulfone                                                                       Theoretical yield                                                                          289.0   2.305 NH  258.0 1.805 NH                                 Calculated equivalent                                                         weight       125               143                                            ______________________________________                                         .sup.1 ARALDITE 6010 from CIBAGEIGY Corp.                                

The diglycidyl ether was charged into a vessel and heated to 100° C.Bisphenol A and NaOH were then added with the temperature maintained at100° C. The pressure was reduced to about 100 mm Hg. and heat increasedto 160° C. and maintained for 2-3 hours until the epoxy value reached0.21-0.22 equivalents per 100 grams. Atmospheric reflux was switched to,the ketone added to dissolve the resin and the system cooled.Thereafter, the diaminodiphenylsulfone was added. The slurry was heatedon distillation to 180° C. and the pressure again reduced to 100 mm Hg.The system was held at 180° C. for three additional hours at which pointthe molten product was discharged.

EXAMPLE II

    ______________________________________                                                   Hardener #3 Hardener #4                                                       Parts       Parts                                                  ______________________________________                                        6010         100.0   0.530 epoxy                                                                             100.0 0.530 epoxy                              Bisphenol A  51.8    0.454 OH  51.8  0.454 OH                                 50% NaOH     0.008             0.008                                          After complete       0.076 epoxy     0.076 epoxy                              reaction                                                                      Methyl isobutyl                                                               ketone       50.0              50.0                                           Methyl ethyl ketone                                                                        51.2              51.2                                           Diamino diphenyl-                                                                          159.8   2.577 NH  126.5 2.041 NH                                 sulfone                                                                       Theoretical yield                                                                          311.6   2.501 NH  278.3 1.964 NH                                 Calculated equivalent                                                         weight       125               142                                            ______________________________________                                    

The diglycidyl ether was charged into a vessel and heated to 115° C.Bisphenol A and NaOH were then added with the temperature maintained at100° C. The pressure was reduced to about 100 mm Hg and heat increasedto 190° C. and maintained at 190° C.-200° C. for three hours until theexpoxy value reached 0.050 equivalents per 100 grams. Atmospheric refluxwas switched to, the ketones added to dissolve the resin and the systemcooled. Thereafter, the diaminodiphenylsulfone was added. The slurry washeated on distillation to 180° C.-185° C. and the pressure again reducedto 100 mm Hg. The system was held at 180° C.-185° C. for threeadditional hours at which point the molten product was discharged.

EXAMPLE III

The following examples are directed to the performance characteristicsof the modified hardeners of Examples I and II and of the processedepoxy resin. Tetraglycidylated methylene dianiline (MY-720 fromCIBA-GEIGY Corp.) was utilized in each instance. A control utilizingunmodified diamino diphenylsulfone hardener was included in the tests.All of the combinations were at an 85% stoichiometry of aminohydrogen toepoxy.

I. The physical properties of the four prepared modified hardeners andof the unmodified hardener are given below:

    ______________________________________                                        HARDENER COMPONENT PROPERTIES                                                           Hardener                                                                     Con-                                                                 Component                                                                              trol   #1       #2     #3     #4                                     ______________________________________                                        Amino-                                                                        hydrogen                                                                      Equivalent                                                                    Weight    62    125      142    125    142                                    (g. equiv.)                                                                   Softening                                                                     Point (°C.)                                                                     --     105-110  105-110                                                                              105-110                                                                              105-110                                Melting                                                                       point (°C.)                                                                     170    --       --     --     --                                     Solution                                                                      viscosity                                                                     60% MEK  --     275-370  400-625                                                                              885-1290                                                                             1290-1760                              (cst)                                                                         ______________________________________                                    

It should be noted that the average molecular weight of the modifiedhardeners increased from #1 to #4 as can be seen from the solutionviscosities. It should be noted that all of the modified versions of thehardener had an improved solubility with the molten MY-720 while purehardener was not as compatible.

II. Flow Characteristics:

Melt viscosities were determined for each of the five systems (Table 2)by placing a known amount of MY-720 into an aluminum dish and heating itto 150° C. To this, the required amount of hardener was added andthoroughly mixed for 142 seconds. The dish was removed from the heat andallowed to cool to room temperature.

Melt viscosities for the mixes were determined on a cone and plateviscometer (Research Equipment, London, Ltd.) at 150° C. The valueobtained by this measurement is an initial viscosity at an elevatedtemperature which bears a relationship to the minimum viscosity obtainedduring the cure cycle. Tests comparing this cone and plate viscosity toa Rheometrics DMA minimum viscosity (2° C./min. heat-up) has shown ahigh positive correlation. The equation describing this relationship is,

Equation (1):

    log[R]=1.59 log [B/4]-1.43

    r=0.999

where:

R=Rheometrics minimum viscosity, cps, for a 2° C./min. heat-up.

B=Cone and plate viscosity, cps, at 150° C.

The table below describes the cone and plate viscosities at 150° C. foreach of the five systems and the projected Rheometrics DMA minimumviscosity based upon Equation (1).

    ______________________________________                                        CONE AND PLATE VISCOSITIES OF 150° C. AND                              PROJECTED RHEOMETRICS MINIMUM VISCOSITY                                       Viscosity                                                                              Cone & Plate Projected Rheometrics DMA                               System   at 150° C. (cps)                                                                    Viscosity (cps)*                                        ______________________________________                                        Control  320          40                                                      1        1520         470                                                     2        2600         1100                                                    3        3500         1800                                                    4        6600         4900                                                    ______________________________________                                         *Minimum viscosity obtained using a 2° C./min. heat rise.         

This data is significant since there is a need within the AerospaceIndusty for a "controlled flow " high performance resin system.Controlled flow may be defined as a higher minimum melt-flow viscosityduring a fixed processing cycle. Such a property is advantageous for lowor no bleed prepreg systems for use as honeycomb skins. The modifiedsystems show varying degrees of melt viscosity increases or "controlledflow" depending upon the molecular weight distribution of the hardener.The data presented above demonstrates this effect with a melt-flowviscosity increase, in system #4, of more than 100 times that of thestandard system.

III Pure Resin Characteristics:

Pure resin castings were prepared by carefully heating the MY-720 to135° C. and slowly stirring in the powdered hardener until a clearmixture was obtained. The combined epoxy and hardener was degassed undera 30 in. Hg vacuum for twenty minutes at 135° C. in order to remove anyair or dissolved gasses. The material was then poured into a sheet moldand cured. The cure schedule and epoxy/hardener proportions for thesystems examined are given below.

    ______________________________________                                        PURE RESIN SYSTEMS                                                            COMPONENTS AND CURE CYCLE                                                              System                                                               Component (pbw)                                                                          Control   1       2     3     4                                    ______________________________________                                        MY-720     100       100     100   100   100                                  Control     44       --      --    --    --                                   #1         --         85     --    --    --                                   #2         --        --      100   --    --                                   #3         --        --      --     85   --                                   #4         --        --      --    --    100                                  ______________________________________                                         Resin Cure:                                                                   2hr/80° C.                                                             1hr/100° C.                                                            4hr/150° C.                                                            7hr/200° C.                                                       

Cured pure resin flexural and tensile data for the five systems wereobtained at room temperature and 150° C. according to ASTM test methodsD-790 and D-638, respectively. In addition, room temperature compressiveproperties were determined by ASTM D-695.

Heat deflection temperatures (HDT) for the resin systems were determinedby ASTM D-648. Thermomechanical analysis (TMA) to determine the glasstransition temperature (Tg) was carried out in the penetration mode witha heat-up of 10° C./min. and a 5 gram loading. These values are givenbelow:

    ______________________________________                                        PURE RESIN PHYSICAL PROPERTIES                                                           System                                                                          Con-                                                             Property     trol    #1      #2    #3    #4                                   ______________________________________                                        Room Temperature:                                                             Tensile Strength(psi)                                                                      8,540   9,230   6,970 12,160                                                                              11,500                               Tensile Modulus(psi)                                                                       542,000 507,000 498,000                                                                             535,000                                                                             515,000                              Tensile Elongation(%)                                                                      1.8     2.0     1.5   2,7   2.6                                  Flexural Strength(psi)                                                                     13,300  19,000  16,970                                                                              20,250                                                                              19,600                               Flexural Modulus(psi)                                                                      499,000 500,000 469,000                                                                             534,000                                                                             508,000                              Compressive                                                                   Strength(psi)                                                                              34,000  29,300  30,500                                                                              33,300                                                                              36,000                               Compressive                                                                   Yield(psi)   29,200  26,400  25,600                                                                              24,300                                                                              23,700                               Compressive                                                                   Modulus(psi) 284,000 275,000 287,000                                                                             315,000                                                                             314,000                              150° C.:                                                               Tensile Strength(psi)                                                                      6,460   8,000   8,800 6,100 6,100                                Tensile Modulus(psi)                                                                       378,000 342,000 358,000                                                                             189,000                                                                             179,000                              Tensile Elongation(%)                                                                      1.9     3.9     3.6   5.9   6.0                                  Flexural Strength(psi)                                                                     12,300  13,400  13,300                                                                              9,000 9,000                                Flexural Modulus(psi)                                                                      387,000 353,000 374,000                                                                             192,000                                                                             202,000                              Heat Deflection                                                               Temperature(C.°)                                                                    238     201     204   200   199                                  Glass Transition                                                              Temperature(C.°)                                                                    177     192     180   174   175                                  ______________________________________                                    

The physical property data for the pure resin systems examinedillustrate the significant property increases for room temperatureflexural and tensile strengths that are obtained for the modifiedsystems with some decrease in thermal capability as observed by HDT.Systems #3 and #4 have the best room temperature tensile propertieswhile systems #1 and #2 show superior tensile properties at elevatedtemperatures. Flexural data indicated that all of the modified systemsare stronger at room temperature than the control with systems #1 and #2having the the best elevated temperature strengths of the modifiedversions. Compressive strengths and moduli for systems #1 through #4 arecomparable to the control while the compressive yield shows a decrease,probably due to a reduction in the crosslink density. Overall, systems#3 and #4 demonstrate the best room temperature static mechanicalproperties, while systems #1 and #2 have the best elevated temperatureproperties.

Impact testing at room temperature was run on the pure resin systems bytwo methods. The first was an unnotched Charpy impact to determine theenergy required to initiate and propagate a fracture. This test was runaccording to ASTM D-256 except that no notch was placed into thespecimen. The second method was a modified Gardner impact where anunrestrained 1"×1"×1/8" specimen was fractured by a falling weighthaving a nose radius of 1/4". The impact strength was measured as theforce at which failure occurred. These values are recorded below alongwith the room temperature and 150° C. tensile elongations.

    ______________________________________                                        IMPACT AND TENSILE ELONGATION                                                 OF THE PURE RESIN                                                                         System                                                            Property      Control   1      2    3    4                                    ______________________________________                                        Room Temperature:                                                             Modified Gardner                                                              (in-lb)       7         7      6    12   8                                    Unnotched Charpy                                                              (ft-lb/in.sup.2)                                                                            5.7       8.2    9.4  8.1  19.0                                 Tensile Elonga-                                                               tion(%)       1.8       2.0    1.5  2.7  2.6                                  150° C.:                                                               Tensile Elonga-                                                               tion(%)       1.9       3.9    3.6  5.9  6.0                                  ______________________________________                                    

Depending upon how impact is measured, whether by tensile elongation,Charpy or a falling ball, the values obtained will vary because eachtest is measuring a different aspect of impact or toughness. All of themodified systems examined demonstrated increased impact and toughness,with systems #3 and #4 having the highest increases.

In order to obtain these increases in physical properties, some loss inHDT (load bearing capability at elevated temperatures) was incurred, butthe glass transition temperature as measured by TMA is not changed forsystems #3 and #4 and is even increased in systems #1 and 190 2.

Humidity testing was carried out on the pure resin systems at 80° C. and95% relative humidity. The moisture pickup is shown below:

    ______________________________________                                        HUMIDITY AGING OF PURE RESIN                                                  AGED UNTIL EQUILIBRIUM (25 DAYS) AT 80° C.                             AND 100% RELATIVE HUMIDITY                                                    SYSTEM            % WEIGHT GAIN                                               ______________________________________                                        CONTROL           4.29                                                        1                 3.28                                                        2                 3.17                                                        3                 3.00                                                        4                 2.80                                                        ______________________________________                                    

The modified systems demonstrate a definite improvement in moistureresistance.

Furthermore, it is noted from the following table that the desiredproperties are substantially maintained even after humidity aging.

    ______________________________________                                        EFFECTS OF HUMIDITY EXPOSURE AT                                               ROOM TEMPERATURE PURE RESIN                                                   MECHANICAL PROPERTIES                                                                    CON-                                                                          TROL  1       2       3     4                                      ______________________________________                                        % WEIGHT GAIN                                                                              4.29    3.28    3.17  3.00  2.80                                 HDT (°C.)                                                                           141     148     133   117   110                                  FLEX:                                                                         STRENGTH (psi)                                                                             13,700  13,900  16,600                                                                              15,500                                                                              19,300                               MODULUS (psi)                                                                              499,800 488,300 477,900                                                                             489,400                                                                             500,500                              TENSILE                                                                       STRENGTH (psi)                                                                             3,900   5,400   4,600 6,500 8,700                                MODULUS (psi)                                                                              446,700 445,800 434,800                                                                             476,100                                                                             465,500                              ELONGATION (%)                                                                             0.9     1.2     1.1   1.4   2.1                                  ______________________________________                                    

A comparison of the above values with those presented in the tableentitled "Pure Resin Physical Properties" reveals that the mechanicalproperties of the modified systems of the instant invention are lesseffected than those of the control. This property retention can thus beattributed to the increased moisture resistance of the instant systems.

IV. Composite Characteristics:

Unidirectional graphite prepreg was prepared from Thornel-300 graphiteyarn (Grade WYP-30, finish UC-309, no twist). The yarn was passedthrough a 30-35% by weight solution of resin/hardener in MEK/Acetone(50/50) and would onto a drum winder yielding a tape with 20 tows/inch,12 feet long and 18 inches wide. The prepreg was allowed to air dry onehour and was then staged for three minutes at 120° C. This gave aprepreg with acceptable drape and tack. The prepreg was cut, layed-upand cured by compression molding. The impregnating solutions and curecycle are given below.

    ______________________________________                                        COMPOSITE IMPREGNATING SOLUTIONS                                              AND CURE CYCLE                                                                          System                                                              Component (pbw)                                                                           Control   1       2     3     4                                   ______________________________________                                        MY-720      100       100     100   100   100                                 Control     44        --      --    --    --                                  #1          --        85      --    --    --                                  #2          --        --      100   --    --                                  #3          --        --      --    85    --                                  #4          --        --      --    --    100                                 MEK         144       185     200   185   200                                 Acetone     144       185     200   185   200                                 ______________________________________                                    

Compression Molding Cure Cycle for Composites:

(1) Room temperature to 176° C. @3° C./min.

(2) Hold 90 minutes at 176° C. Apply 100 psi at the gel point (10-20minutes into the hold)

(3) Cool to room temperature

(4) Post cure 4 hours at 205° C.

All of the laminates manufactured for test purposes were analyzed forvoid content by ASTM methods D-3171, D-2734 and D-792. All of thefabricated panels were found to have zero voids. The composite datapresented has been corrected to a 30 weight percent resin content.

Twenty ply, 0° panels were prepared from each of the systems describedabove. From these laminates, short beam shear specimens were obtainedand tested according to ASTM D-2344 at room temperature, -59° C., and93° C. 0° flexural properties were obtained from 10 ply panels andtested by ASTM D-790 at room temperature, -59° C., and 93° C. Fourteenply matrix tensiles, oriented at +45/90/-45/90 and tested in the 0°direction according to ASTM D-3039 at room temperature and -59° C., wereused to measure the combined effects of shear and matrix strength. Shortbeam shear, flexural and matrix tensile data appear below.

    ______________________________________                                        PRELIMINARY COMPOSITE PROPERTIES                                                         System                                                                          Con-                                                             Property     trol    1       2     3     4                                    ______________________________________                                        Short Beam Shear,                                                             0° (ksi)                                                               -59° C.                                                                             11.2    9.7     11.2  10.0  10.6                                 room temperature                                                                           10.5    10.5    10.5  9.5   12.0                                 93° C.                                                                              9.4     9.1     9.1   8.2   11.5                                 Flexural Strength,                                                            0° (ksi)                                                               -59° C.                                                                             209     --      263   263   240                                  room temperature                                                                           228     241     219   224   234                                  93° C.                                                                              227     --      251   240   216                                  Flexural Modulus, 0°                                                   (psi × 10.sup.6)                                                        -59° C.                                                                             13.2    --      15.4  14.1  16.2                                 room temperature                                                                           14.8    14.6    15.0  14.1  13.6                                 93° C.                                                                              14.9    --      17.4  16.4  15.3                                 Matrix Tensile                                                                Strength (ksi)                                                                -59° C.                                                                             13.6    22.0    13.7  25.8  14.7                                 room temperature                                                                           14.7    24.0    16.2  30.0  14.6                                 Matrix Tensile                                                                Modulus (ksi)                                                                 -59° C.                                                                             498     385     390   521   453                                  room temperature                                                                           539     424     425   594   319                                  Matrix Tensile                                                                Elongation (%)                                                                -59° C.                                                                             4.3     5.6     4.5   5.6   5.0                                  room temperature                                                                           3.5     6.1     5.2   5.3   5.2                                  ______________________________________                                    

Although the processing used to manufacture the test panels was notnecessarily optimized, the data presented above for each of the fivesystems is considered to be valid in comparison of the systems. Themodified hardener shear properties seem to be similar to those of thestandard hardener and the flexural properties, which are highlydependent on the fiber content, are also similar.

Matrix tensiles were run on all five systems. This test measures thecombined effects of the resin matrix and shear properties of thecomposite. Such a measurement may be interpreted as an indication oftoughness with increased strength and elongation to break being relatedto an increase in toughness. A real difference appears in this data,where all of the modified systems shown improvements over the control,but systems #1 and #3 appear to be the best.

Summarizing, it is seen that this invention provides novel, modifiedhardener systems for epoxy resins which exhibit excellent performancecharacteristics. Variations may be made in preparation, procedures, andmaterials without departing from the scope of the invention as definedby the following claims.

What is claimed is:
 1. A hardener for polyfunctional epoxy resinscomprising the adduct obtained from the reaction of a diaminodiphenylsulfone corresponding to the formula ##STR4## wherein R₁, R₂, R₃and R₄ are independently hydrogen, straight and branched chain alkyl of1 to 12 carbons or halogen,and a diglycidyl ether of a polyhydricphenol; said hardener having from about 2.5 to 100 equivalents ofaminohydrogen per equivalent of epoxy.
 2. The hardener of claim 1,wherein said sulfone is diamino diphenyl sulfone.
 3. The hardener ofclaim 1, wherein said diglycidyl ether is selected from the groupconsisting of diglycidyl ethers of bisphenols corresponding to theformula ##STR5## wherein m is 0-50 and X is --CH₂ --, ##STR6## and thediglycidyl ethers of resorcinol, catechol and hydroquinone.
 4. Thehardener of claims 2 or 3, wherein said diglycidyl ether is thediglycidyl ether of bisphenol A.
 5. A curable mixture comprising (a) apolyepoxide compound and (b) a hardener according to claims 1, 2 or 3.6. The curable mixture of claim 5, wherein said hardener and saidpolyepoxide compound are present in stoichiometric amounts ±50%.
 7. Thecurable mixture of claim 5, wherein said polyepoxide compound isselected from the group consisting of epoxide resins based on polyhydricphenols, hydantoin epoxide resins, polyglycidyl esters, glycidylatedaromatic amines, glycidylated aminophenols and cycloaliphatic epoxyresins.
 8. The curable mixture of claim 5 wherein said polyepoxidecompound is tetraglycidylated methylene dianiline.
 9. A curable mixturecomprising (a) tetraglycidylated methylene dianiline and (b) a hardenercomprising the reaction product of diamino diphenylsulfone anddiglycidyl ether of bishpenol A; said hardener being present at 85%stoichiometry relative to said dianiline.
 10. The product obtained bycuring the mixture of claim 5 at elevated temperatures.
 11. The productobtained by curing the mixture of claim 9 at elevated temperatures.